Length of Analog Audio Cables? - AVS Forum
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post #1 of 14 Old 11-06-2013, 09:49 AM - Thread Starter
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How long can you run analog (RCA) cables from source to receiver without loosing too much SQ?

Can I run it 50 ft?
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post #2 of 14 Old 11-06-2013, 10:33 AM
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The maximum length you can have before losing high frequencies depends on a number of things, so there's no single answer. But I'd say 50 feet is too long for typical consumer gear. The main two issues are the sending device's output impedance, and the capacitance of the wire. However, a headphone output might be able to drive 50 feet.

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post #3 of 14 Old 11-06-2013, 10:35 AM
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Hi Jah,

Fifty feet is not a problem for sound quality. I've run hundreds of feet. It could potentially be a problem for hum.

If your devices are fifty feet apart, there is the possibility that they could be at slightly different ground levels, and that could cause hum. The solution could be a simple ground wire between devices (assuming the difference is small), or an isolation transformer.

Also, if that fifty feet of cable is running along other cables that emit electrical noise, there is a possibility of picking up that noise in the audio. That also can be mitigated.

So my suggestion is to try it. Chances are you will be fine.


Edit:
Ethan and I cross-posted. He has a good point about cable capacitance. I typically use low-capacitance cable.
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post #4 of 14 Old 11-06-2013, 11:13 AM
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Most consumer grade unbalanced cable uses a spiral wrapped shield as opposed to a tight braid. The spiral wrap is the cheapest style available and is usually fine for lengths up to 6 ft. With a fifty foot run it is possible to get a clean usable signal but I personally would opt to spend a little more money and use balancing transformers and a good quality balance cable for each channel. Keep in mind that most stores like radio shack and guitar center sell balanced cable BUT it too is a spiral wrap shield. Belden, Gepco, Mogami and Canare are the best source for low noise quality shielded cable stock.
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post #5 of 14 Old 11-06-2013, 12:07 PM
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Most inexpensive consumer cable is simply small RF cable that in an unterminated environment (i.e. audio) exhibits around 20 pF/ft capacitance. Thus 50 feet yields roughly 1 nF (50 * 20 pF) of capacitance. The load is usually high-impedance, 10k or more, and the sources I have seen range from around 100 ohms to 1k ohms for consumer gear (usually a series R at the buffer output for stability and short-circuit protection). At 100 ohms the run would have about 1.6 MHz bandwidth, and about 160 kHz with a 1k-ohm source. My guess, which seems in line with the experts above, is that noise will be the biggest issue for such a long run. As Giz sez a tight braid is better; even better cables will use a foil shield for 100% coverage. I would also go balanced for such a long run if at all possible.
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post #6 of 14 Old 11-08-2013, 05:30 PM
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I saw this response in another forum about long interconnects:

It's pretty rare for audio cables to get into that range, those kinds of lengths. Certainly in the consumer side, because of the high source impedance, the lengths before significant loss are very short. On all-PVC (high capacitance) cables only a few feet. I'm always surprised when I see a 50 ft. or 100 ft. RCA cable in Radio Shack or somewhere. Surely this is the "most returned" item in the store!

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post #7 of 14 Old 11-09-2013, 03:35 AM
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Quote:
Originally Posted by jah.volunteer View Post

How long can you run analog (RCA) cables from source to receiver without loosing too much SQ?

Cables from less than a foot long to 100's of feet long can be problematical or operate flawlessly, depending on the circumstance.

The idea that longer cables can cause more problems is correct, but the idea that short cables are never a problem is false. The idea that long cables (e.g. 50 feet or more) always cause audible sound quality loss is false.
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Can I run it 50 ft?

Probably, and without noise pick up or sound quality loss.

But regardless of the cable's length, it is not always a slam dunk.

My best advice is hook it up using quality connectors and cabling, and see what happens.

If you have audible problems, post them and the equipment and setup involved, and we'll try to fix you up. Many of us run audio cables for 100 feet or more, so we know how to do it.
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post #8 of 14 Old 11-13-2013, 12:31 PM - Thread Starter
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Thanks for the replies everyone.

Would using audio baluns (RCA >CAT5 >RCA) with the CAT5 covering 95% of the run help to eliminate the potential hum or other interference?

If it helps, this is the setup I'm considering:

PC Audio > USB > DAC > RCA Analog > Receiver (40-50ft away)
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post #9 of 14 Old 11-13-2013, 04:32 PM
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Quote:
Originally Posted by jah.volunteer View Post

Thanks for the replies everyone.

Would using audio baluns (RCA >CAT5 >RCA) with the CAT5 covering 95% of the run help to eliminate the potential hum or other interference?

If it helps, this is the setup I'm considering:

PC Audio > USB > DAC > RCA Analog > Receiver (40-50ft away)

Your best bet is to run as much of the distance in the digital domain.

http://www.monoprice.com/Product?c_id=103&cp_id=10303&cs_id=1030312&p_id=7533&seq=1&format=2

Another approach is If the AVR has a digital andio input, use a digital audio output from the PC.
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post #10 of 14 Old 11-13-2013, 05:06 PM - Thread Starter
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That's a fantastic suggestion arnyk and it sounds like potentially the best option. I could then just put the DAC at the receiver end rather than the PC end.

As to your second suggestion, I will be using a networking AVR, however, I intend to run multiple zones at once and from what I understand, most networking AVRs can only send a digital input to one zone at a time (as they only have one built in DAC).

Perhaps I am misunderstanding your second option (or misunderstanding how a DLNA networked AVR works)

....or perhaps running a straight digital audio feed is different than running a DLNA network feed to the AVR?
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post #11 of 14 Old 11-13-2013, 05:31 PM
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Quote:
Originally Posted by jah.volunteer View Post

That's a fantastic suggestion arnyk and it sounds like potentially the best option. I could then just put the DAC at the receiver end rather than the PC end.

As to your second suggestion, I will be using a networking AVR, however, I intend to run multiple zones at once and from what I understand, most networking AVRs can only send a digital input to one zone at a time (as they only have one built in DAC).

That can be true.
Quote:
....or perhaps running a straight digital audio feed is different than running a DLNA network feed to the AVR?

It is different, but go with what you understand the best and think will work the best.

I often provide multiple answers so that the reader can make his own choices. One it not necessarily better than the other.
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post #12 of 14 Old 11-15-2013, 07:00 PM
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I suggest the most simple approach as starters if you're running line level signals.

In my system there is a run of 35ft, using nothing but some inexpensive Belden shielded twisted pair in an unbalanced configuration. No problems at all with noise or crappy sound. Today I realize that a coaxial cable may have been a better choice for an unbalanced run, but having zero problems with this one I have not made the change.

Just because there is a knob doesn't mean you should turn it.
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post #13 of 14 Old 11-16-2013, 09:58 AM
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It seems like a digital cable would be the best solution, but those long USB cables have to be active devices to span that distance and must have a powered repeater in the center. That one seems to have good reviews, but I had problems with one of those cables - it would keep dropping out and losing connection. My friend tried to use one to connect to his telescope and had so many problems that he finally threw it out.

I would just use a high quality, low capacitance analog cable. As another reply said, the simplest solution is most often the best solution. I have a 35ft run and I too didn't want to have any problems so I did some research and found these cables from Blue Jeans Cables - they aren't cheap but they are very high quality and very low capacitance. Mine was an in-wall run and I didn't want any problems.

Capacitance, conductor to shield: 12.2 pF/ft:
http://www.bluejeanscable.com/store/audio/index.htm

This is a very good discussion on the effect of long length audio cables:
http://www.bluejeanscable.com/store/audio/LC1-design-notes.htm

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post #14 of 14 Old 11-18-2013, 11:37 AM - Thread Starter
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Thanks to everyone for all of the replies. mtn-tech, I may very well go that route. My only reservation would be the cost. On the flip side, I could end up spending $100-$150 on other solutions that don't work before I realize that the low-capacitance RCA cables are the best bet.

Are you aware of any active USB extender/booster cables that may work better than the passive ones listed on Monoprice?

I'm also curious about using audio baluns to run the analog signal over CAT5 for the majority of the run. If anyone reads this and has implemented this solution, I'd love to hear about your results.
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